Many methods have been used to produce a metallic-looking image on a substrate. For the most part, these methods involve the use of metallic pigments and metal-containing inks. U.S. Pat. No. 4,233,195 to Mills, U.S. Pat. No. 5,912,283 to Hashizume et al., U.S. Pat. No. 5,662,738 to Schmid et al., and U.S. Pat. No. 5,766,335 to Bujard et. al. describe pigments and ink formulations that incorporate metallic, usually aluminum, particles. While different approaches have been followed to provide enhanced color and pigment variation, the inks and pigments used are typically costly and require complicated and expensive procedures. For example, U.S. Pat. No. 5,370,976 to Williamson et al. describes a metallic color printing process wherein the image is produced using a four-color separation process, involving metallic gold and/or metallic silver separations, and an electronic masking system.
Other processes have been developed for producing a metallic-looking image without the use of metallic pigments. U.S. Pat. No. 5,656,331 to Kline, for example, describes a printed substrate having a metallic finish where the metallic appearance is achieved by applying a first layer having the desired final color pattern, a second layer comprising a moire dispersion pattern and a third coating of water pearl. Complex thermal processing methods have also been used. For example, U.S. Pat. No. 5,564,843 to Kawaguchi describes a method of producing a reflective image by printing the image on the surface of a film using a thermal print head and then affixing the film onto a reflective surface.
Reflective surfaces to form metallic-looking images have also been used, primarily in the marketing and display industries. U.S. Pat. No. 5,106,126 to Longobardi et al. describes a process for reverse printing on a transparent facing material such as a MYLAR® polyester sheet or a glass sheet. The printing must be done as a mirror image and the printing steps must be performed in an order that is the reverse of the order used in conjunction with conventional printing, making it difficult to use standard printing equipment without substantial modification. Also, this method is quite costly.
A more direct method is provided in U.S. Pat. No. 5,733,634 to Karel wherein a metallic-looking image is generated by first applying a coating of a white pigment to the surface of a reflective substrate, wherein the applied pigment has varying density across the surface, and then applying a coating of a colored pigment, also in varying density across the surface. Those surface areas having a lower density of white and colored pigments have a metallic-looking appearance, as the reflective substrate is visible through the coating layers. This method is effective, it requires a separate screened application of the white dots and is not suitable for use in conventional ink-jet printing or in any other consumer usable image production method.
Accordingly, there is a need in the art for a simple and inexpensive process for the printing of light-emitting, reflective or metallic-looking images.